JPH0955558A - Semiconductor laser device - Google Patents

Abstract

Provided is a semiconductor laser device capable of improving device characteristics in high temperature operation and preventing a decrease in light emission efficiency. An n-type first substrate is formed on an n-type GaAs substrate 101.
The clad layer 102, the active layer 103, and the p-type second clad layer 104 are formed in this order. An n-type current / light confinement layer 105 having a stripe-shaped groove portion 106 thereon is formed.
And the p-type third cladding layer 107 is formed so as to fill the stripe-shaped groove portion 106. The n-type current / light confinement layer 105 contains Si as a dopant,
The n-type first cladding layer 102 does not contain Si as a dopant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device used for optical disks and the like.

[0002]

[Prior art]

(Prior Art Example 1) Conventionally, in a semiconductor laser device, a buried hetero structure as shown in FIG. 8 has been proposed in order to improve the current and light confinement efficiency in the lateral direction (direction horizontal to the substrate). This semiconductor laser device comprises a first M-type semiconductor on an n-type GaAs semiconductor substrate 501.
N-type Al _0.5 G by OCVD (metal organic chemical vapor deposition) method
a _0.5 As first cladding layer 502 (carrier concentration 1 × 1
0 ¹⁸ cm ^-3 , dopant Se), non-doped active layer 50
3, p-type Al _0.5 Ga _0.5 As second cladding layer 504 (carrier concentration 5 × 10 ¹⁷ cm ⁻³ , dopant Zn) and n-type GaAs current optical confinement layer 505 (carrier concentration 3
× 10 ¹⁸ cm ⁻³ and dopant Se) are successively grown. A stripe-shaped groove 506 is formed in the n-type current / light confinement layer 505 so as to reach the p-type second cladding layer 504, and the second MO is formed so as to fill the groove 506.
P-type Al _0.5 Ga _0.5 As third cladding layer 507 (carrier concentration 1 × 10 ¹⁸ cm ⁻³ , dopant Z
n) and a p-type GaAs contact layer 508 (carrier concentration 3 × 10 ¹⁸ cm ⁻³ , dopant Zn) are formed. In such a semiconductor laser device, Se is used as the n-type dopant and Zn is used as the p-type dopant.
Is generally used. In addition, the p-type second cladding layer 50
The layer thickness of No. 4 is set in the range of 0.05 to 0.6 μm so that the current and the light can be effectively confined.

(Conventional example 2) By the way, Fujii et al.
At the E VII conference (1994), I made the following report. On an n-type GaAs substrate, an n-type Al _0.5 Ga _0.5 As layer (carrier concentration 1 × 10 ₅ ) was formed by MOCVD.
¹⁸ cm ^-3 , dopant Se) and p-type Al _0.5 Ga _0.5
As layer (carrier concentration 1 × 10 ¹⁸ cm ⁻³ , dopant Z
n, layer thickness 1.25 μm) and an n-type GaAs layer are sequentially grown. When Se is used as the dopant for the n-type GaAs layer, when the carrier concentration of Se becomes 4 × 10 ¹⁸ cm ⁻³ or more, the p-type Al _0.5 Ga _0.5 As layer is changed to the n-type Al _0.5 Ga layer.
The diffusion of Zn into the _0.5 As layer and the n-type GaAs layer is increased. On the other hand, the dopant of the n-type GaAs layer is S
When i is set, the carrier concentration of Si is 4 × 10 ¹⁸ cm ⁻³
The diffusion of Zn is relatively small even if it becomes 6 × 10 ¹⁸ cm
^{If it is -3} or more, Zn diffusion increases as in Se.

(Conventional example 3) On the other hand, Neave et al.
l.Phys.A32 (1983) 195., when Si was used as an n-type dopant, the carrier concentration was 3 × 10 ¹⁸ cm ^−3.
It is reported that the luminous efficiency drops sharply when the above is reached.

[0005]

However, the above-mentioned conventional example 1
3 to 3, there are the following problems.

In the semiconductor laser device of Conventional Example 1, the n-type G
An n-type first cladding layer 502, an active layer 503, a p-type second cladding layer 504, and an n-type current / light confinement layer 505 are sequentially grown on the aAs substrate by the first MOCVD method. At this time, Zn contained in the p-type second clad layer 504 as a dopant is not included in the n-type first clad layer 5 on both sides.
02 and the n-type current / light confinement layer 505, and as a result, the carrier concentration of the p-type second cladding layer 504 decreases. As a result, the barrier of the p-type second cladding layer 504 with respect to the carriers injected into the active layer 503 is lowered, and p
Carriers leak to the mold second cladding layer 504 side. Since such carrier leakage occurs remarkably during high temperature operation, there is a problem that the characteristics of the semiconductor laser device deteriorate during high temperature operation.

Further, in Conventional Example 2, an n-type AlGaAs layer and a p-type Al are formed on the n-type GaAs substrate by MOCVD.
When sequentially growing a GaAs layer and an n-type GaAs layer,
It is better to use S as the dopant for the n-type GaAs layer.
It is shown that the diffusion of Zn, which is a dopant of the p-type AlGaAs layer, is less than that of using e. However, this structure is different from the semiconductor laser device structure because there is no layer corresponding to the active layer of the semiconductor laser device between the n-type AlGaAs layer and the p-type AlGaAs layer. Also, p
The type AlGaAs layer has a layer thickness of 1.25 μm, which is much thicker than the typical layer thickness of the second cladding layer in the semiconductor laser device structure of 0.05 μm to 0.6 μm. Furthermore, the carrier concentration of the p-type AlGaAs layer is unknown. Therefore, it is not clear what happens to the diffusion state of Zn when applied to the semiconductor laser device structure.

Further, in Conventional Example 3, as described above,
It has been reported that when Si is doped at a high concentration as an n-type dopant, the luminous efficiency is reduced. Therefore,
When Si is used as the dopant of the n-type cladding layer adjacent to the active layer in order to improve the characteristics of the semiconductor laser device in high temperature operation, Si diffuses into the active layer, and the Si diffuses the light emission efficiency inside the active layer. There is a problem that it will decrease.

The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a semiconductor laser device capable of improving the device characteristics in high temperature operation and preventing a decrease in light emission efficiency. To do.

[0010]

In a semiconductor laser device of the present invention, an n-type first cladding layer, an active layer and a p-type second cladding layer are formed in this order from the substrate side on an n-type semiconductor substrate, In the semiconductor laser device, the n-type current / light confinement layer having a stripe-shaped groove is formed on the second clad layer, and the p-type third clad layer is formed so as to fill the stripe-shaped groove. The confinement layer contains Si as a dopant and the first cladding layer does not contain Si as a dopant, which achieves the above object.

In the semiconductor laser device of the present invention, an n-type first clad layer, an active layer and a p-type second clad layer are formed in this order from the substrate side on an n-type semiconductor substrate, and on the second clad layer. In the semiconductor laser device, a p-type third clad layer having a ridge stripe shape is formed in the semiconductor laser element, and an n-type current light confinement layer is formed so as to sandwich both sides of the third clad layer having a ridge stripe shape. The confinement layer contains Si as a dopant and the first cladding layer does not contain Si as a dopant, which achieves the above object.

The thickness of the second cladding layer is 0.05 μm
It is desirable that it is not less than 0.6 μm.

The band gap of the current / light confinement layer is equal to or smaller than the band gap of the active layer, and the carrier concentration of the current / light confinement layer is 1 × 10 ¹⁸ cm ⁻³ or more and 5 × 10.
^It is preferably ¹⁸ cm ^-3 or less.

The band gap of the current / light confinement layer is larger than the band gap of the active layer, and the carrier concentration of the current / light confinement layer is 1 × 10 ¹⁷ cm ⁻³ or more and 5 × 10.
^It is preferably ¹⁸ cm ^-3 or less.

The dopant of the first cladding layer is preferably a group VI atom.

The operation of the present invention will be described below.

In the present invention, the n-type current / light confinement layer contains Si as a dopant. Therefore, when the n-type first clad layer, the active layer, the p-type second clad layer and the n-type current / light confinement layer are grown on the n-type GaAs substrate, diffusion of the dopant of the p-type second clad layer, for example, Zn is performed. Can be suppressed.

Since the n-type first cladding layer adjacent to the active layer does not contain Si as a dopant,
Even if the dopant atoms diffuse from the mold first clad layer to the active layer, the luminous efficiency is not reduced.

The thickness of the p-type second cladding layer is 0.05 μm
When the thickness is 0.6 μm or less, current and light can be efficiently confined.

When the band gap of the n-type current / light confinement layer is set to be equal to or less than that of the active layer and the carrier concentration of the light confinement layer is set to 1 × 10 ¹⁸ cm ⁻³ or more and 5 × 10 ¹⁸ cm ⁻³ or less, or n -Type current / light confinement layer has a bandgap larger than that of the active layer, and the current / light confinement layer has a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ or more and 5 × 1.
When it is 0 ¹⁸ cm ⁻³ or less, current and light can be sufficiently confined and the carrier concentration of the p-type second cladding layer can be sufficiently increased.

The dopant for the first cladding layer is S
When a group VI atom such as e, S, or Te is used, the luminous efficiency does not decrease, so that the deterioration of device characteristics can be prevented.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 shows a sectional view of a semiconductor laser device of Embodiment 1.

In this semiconductor laser device, an n-type Al _0.5 Ga _0.5 As first cladding layer 102 (layer thickness 1.0 μm, carrier concentration 1 × 10 ¹⁸ cm) is formed on an n-type GaAs substrate 101.
^-3 , dopant Se), non-doped Al _0.14 Ga _0.86 A
s active layer 103 (layer thickness 0.08 μm), p-type Al _0.5 G
a _0.5 As second cladding layer 104 (layer thickness 0.3 μm, dopant Zn) and n-type GaAs current light confinement layer 1
05 (layer thickness 0.6 μm, carrier concentration 3 × 10 ¹⁸ c
m ⁻³ , dopant Si) is formed.

A stripe-shaped groove 106 is formed in the center of the n-type current / light confinement layer 105 so as to reach the p-type second cladding layer 104, and the p-type Al _0.5 Ga _0.5 As is buried in the groove 106. A third clad layer 107 (layer thickness 1.5 μm) is formed. On top of that, p-type G
An aAs contact layer 108 (layer thickness 1.5 μm) is formed.

Further, p is formed on the p-type contact layer 108.
A mold electrode 109 is formed, and an n-type electrode 110 is formed on the n-type GaAs substrate 101 side.

This semiconductor laser device can be manufactured as follows.

First, on the n-type GaAs substrate 101, the first
The n-type first cladding layer 10 was formed by the MOCVD method for the first time.
2, non-doped active layer 103, p-type second cladding layer 10
4. The n-type current / light confinement layer 105 is laminated.

Next, a stripe-shaped groove 106 is formed in the central portion of the current / light confinement layer 105 so as to reach the p-type second cladding layer 104, and the second MOCVD method is performed so as to fill the groove 106. Thus, the p-type third cladding layer 107 is formed, and subsequently the p-type contact layer 108 is laminated.

After that, a p-type electrode 109 is formed on the upper surface of the contact layer 108, and an n-type electrode 110 is formed on the lower surface of the substrate 101, and the cavity length is adjusted to 250 μm by the cleavage method, and the reflectance of the cavity end face is adjusted. Of Al ₂ O ₃ to be 30%
Form a film.

In the semiconductor laser device of this embodiment, the band gap of the current / light confinement layer 105 is equal to or less than the band gap of the active layer 103. Therefore, the light generated in the active layer 103 is absorbed by the current / light confinement layer 105, and the light is mainly confined in the active layer immediately below the stripe groove 106. In this semiconductor laser device, the p-type electrode 109
When a forward voltage was applied between the n-type electrode 110 and the n-type electrode 110, the threshold current was 40 mA, and the slope efficiency of the current-light output characteristics was 0.3 W / A.

Room temperature 20 of the semiconductor laser device of this embodiment
Table 1 below shows characteristic temperatures at 80 ° C. and a high temperature of 80 ° C., and a device life when light output of 5 mW was performed at a high temperature of 80 ° C. As a comparative example, a conventional semiconductor laser device containing Se as a dopant of the current / light confinement layer 105 is also shown.

[0033]

[Table 1]

In Table 1 above, the characteristic temperature T0 is 80
The following formula (1) is obtained from the ratio of the threshold current Ith (80 ° C.) at 20 ° C. and the threshold current Ith (20 ° C.) at 20 ° C.
Is defined as The larger T0 is, Ith (80
The ratio of (° C.) to Ith (20 ° C.) becomes close to 1, and the increase in current at high temperature is suppressed.

Ith (80 ° C.) / Ith (20 ° C.) = Exp {(80 ° C.-20 ° C.) / T0} (1) Further, the device life is determined by the operating current of the semiconductor laser device at the initial operating current. It is the running time when it increases by 20%.

As can be understood from Table 1 above, the semiconductor laser device of the first embodiment using Si as the dopant for the n-type current / light confinement layer has a characteristic temperature higher than that of the conventional semiconductor laser device using Se. Is large and the increase in current at high temperatures is suppressed, so the device life during high temperature operation is 3
It has been improved more than twice.

The reason why such a result is obtained can be considered as follows.

The characteristic temperature of the semiconductor laser device is the p-type second temperature.
It depends on the carrier concentration of the cladding layer 104. For example, if the carrier concentration of the p-type second clad layer 104 is low, the barrier of the p-type second clad layer 104 with respect to the carriers injected into the active layer 103 is low, so that the carriers are on the p-type second clad layer 104 side. Leak out. Such carrier leakage is particularly noticeable during high temperature operation, so
During high temperature operation, the current increases and the device life decreases. Experimental studies have revealed that the carrier concentration of the p-type second cladding layer 104 needs to be 5 × 10 ¹⁷ cm ⁻³ or more in order to prevent the carrier leakage.

In the manufacture of the semiconductor laser device as described above, the carrier concentration of the n-type current / light confinement layer 105 at the end of the first MOCVD growth is changed to be equal to the carrier concentration of the p-type second cladding layer 104. The relationship with the layer thickness was measured. FIG. 2 shows the measurement result of the semiconductor laser device according to the first embodiment. FIG. 9 shows the measurement result of the conventional semiconductor laser device using Se as the dopant of the current / light confinement layer 105.

In the conventional semiconductor laser device, as shown in FIG. 9, the carrier concentration of the p-type second cladding layer is 2.0 ×.
Despite growing at a setting of 10 ¹⁸ cm ^-3 , during the growth, the dopant Zn diffuses to both sides of the active layer and the n-type first cladding layer and the n-type current and light confining layer. Therefore, the carrier concentration of the p-type second cladding layer is lowered.

As shown in FIG. 9, in the above conventional semiconductor laser device, in order to make the carrier concentration of the p-type second cladding layer 5 × 10 ¹⁷ cm ^-3 or more, the n-type current light containing the dopant Se is used. Carrier concentration of confinement layer is 1 × 10
It may be less than ¹⁸ cm ^-3 . However, when the carrier concentration of the n-type current / light confinement layer is less than 1 × 10 ¹⁸ cm ⁻³ , n
The carriers generated by the light absorbed in the type current / light confinement layer are less likely to recombine in the n-type current / light confinement layer. When the carriers diffuse to generate a potential, the current-light confinement layer is turned on similarly to the thyristor, and the current cannot be confined. Therefore, in the conventional semiconductor laser device, n-type carrier concentration of the current light confining layer by less than 1 × 10 ¹⁸ cm ^-3, p-type second carrier concentration of the cladding layer 104 5 × 10 ¹⁷ cm ^-3 You can't do more.

On the other hand, when the carrier concentration of the n-type current / light confinement layer is 1 × 10 ¹⁸ cm ⁻³ or more, the carrier concentration of the p-type second cladding layer is 5 × 10 ¹⁷ cm ⁻³ or more, p
The layer thickness of the mold second clad layer may be greater than 0.6 μm. However, if the layer thickness of the p-type second clad layer is made thicker than 0.6 μm, the proportion of the light emitted from the active layer reaching the n-type current / light confinement layer decreases, so that the light cannot be confined. In addition, the p-type second cladding layer is 0.05
If the thickness is less than μm, the carrier concentration in the p-type second cladding layer is lowered due to the diffusion of the dopant from the n-type current / light confinement layer, resulting in insufficient current confinement.

As described above, in the conventional semiconductor laser device, the carrier concentration of the n-type current / light confinement layer 105 is 1.
If the p-type second clad layer 104 has a layer thickness of × 10 ¹⁸ cm ⁻³ or more and a thickness of 0.05 μm or more and 0.6 μm or less,
The carrier concentration of the clad layer 104 cannot be 5 × 10 ¹⁷ cm ⁻³ or more.

Even if the carrier concentration of the p-type second cladding layer is set to 2.0 × 10 ¹⁸ cm ^-3 or more, the diffusion of the dopant Zn during the growth is further increased. The carrier concentration of the second cladding layer is 5 × 10 ¹⁷
It cannot be more than cm ^-3 .

Therefore, in the conventional semiconductor laser device using Se as the dopant of the n-type current / light confinement layer, the carrier concentration of the p-type second cladding layer is 5 × 10 ¹⁷ while sufficiently confining the current and light. Since it cannot be more than cm ⁻³ , the increase in current during high temperature operation cannot be suppressed.

On the other hand, in the semiconductor laser device of this embodiment, as shown in FIG. 2, the carrier concentration of the p-type second cladding layer 104 decreases during growth, but it is lower than that of the conventional semiconductor laser device. The degree of decline is clearly small. This is because diffusion of the dopant Zn of the p-type second cladding layer 104 to the adjacent layer was suppressed by using Si as the dopant of the n-type current / light confinement layer 105.

In the semiconductor laser device of this embodiment,
The carrier concentration of the p-type second cladding layer 104 is set to 5 × 10 ¹⁷
In order to make it cm ⁻³ or more, the carrier concentration of the n-type current / light confinement layer 105 containing the dopant Si is 5 × 10 ¹⁸ c.
It may be m ^-3 or less. In addition, the n-type current / light confinement layer 1
Since the bandgap of No. 05 is less than the bandgap of the active layer 103, in order to sufficiently confine the current, n
Carrier concentration of the photocurrent confinement layer 105 is 1 × 10 ¹⁸
It must be at least cm ^-3 . Further, the layer thickness of the p-type second cladding layer 104 is preferably 0.05 μm or more and 0.6 μm or less in order to sufficiently confine current and light.

As shown in FIG. 2, in the semiconductor laser device of this embodiment, the carrier concentration of the n-type current / light confinement layer 105 is 1 × 10 ¹⁸ cm ⁻³ or more and 5 × 10 ¹⁸ cm ⁻³ or less, and the p-type The p-type second cladding layer 10 is provided under the condition that the layer thickness of the second cladding layer 104 is 0.05 μm or more and 0.6 μm or less.
The carrier concentration of No. 4 can be 5 × 10 ¹⁷ cm ⁻³ or more.

Therefore, it is possible to suppress the leakage of carriers from the active layer 103 to the p-type second cladding layer 104 at high temperature, reduce the high temperature operating current, and improve the device life at high temperature. In this case, the n-type current / light confinement layer 10
Since the carrier concentration of No. 5 is sufficiently high, the carriers generated by the light absorbed in the n-type current / light confinement layer 105 can be recombined in the n-type current / light confinement layer 105, and the current can be sufficiently confined. In addition, the p-type second cladding layer 1
The layer thickness of 04 is a thickness suitable for confining current and light.

Further, in the semiconductor laser device according to the first embodiment, the n-type first cladding layer 10 adjacent to the active layer 103 is provided.
Se is used as the second dopant without using Si. The Se dopant does not deteriorate the light emission efficiency even if it diffuses from the n-type first cladding layer 102 to the active layer 103, and thus it is possible to prevent the deterioration of the characteristics of the semiconductor laser device.

(Second Embodiment) FIG. 3 shows a sectional view of a semiconductor laser device according to a second embodiment.

In this semiconductor laser device, an n-type Al _0.6 Ga _0.4 As first cladding layer 202 (layer thickness 1.0 μm, carrier concentration 1 × 10 ¹⁸ cm) is formed on an n-type GaAs substrate 201.
^-3 , dopant Se), non-doped Al _0.14 Ga _0.86 A
s active layer 203 (layer thickness 0.06 μm), p-type Al _0.6 G
a _0.4 As second cladding layer 204 (layer thickness 0.35 μm,
Carrier concentration 8 × 10 ¹⁷ cm ^-3 , dopant Zn), p
Type GaAs first etching stop layer 205 (layer thickness 0.
003 μm, carrier concentration 8 × 10 ¹⁷ cm ⁻³ , dopant Zn), p-type Al _0.6 Ga _0.4 As second etching stop layer 206 (layer thickness 0.02 μm, carrier concentration 8 × 1)
0 ¹⁷ cm ^-3 , dopant Zn) and n-type Al _0.1 Ga
_{A 0.9} As current / light confinement layer 207 (layer thickness 0.6 μm, carrier concentration 2 × 10 ¹⁸ cm ⁻³ , dopant Si) is formed.

A stripe-shaped groove 208 is formed in the center of the n-type current / light confinement layer 207 so as to reach the p-type first etching stop layer 205, and p-type Al _0.5 Ga _0.5 is formed so as to fill the groove 208. As third clad layer 2
09 (layer thickness 1.5 μm) is formed. On top of that, a p-type GaAs contact layer 210 (layer thickness 1.5 μm
m) is formed.

Further, p is formed on the p-type contact layer 210.
A mold electrode 211 is formed, and an n-type electrode 212 is formed on the n-type GaAs substrate 201 side.

This semiconductor laser device can be manufactured as follows.

First, on the n-type GaAs substrate 201, MO
By the first growth using the CVD method, the n-type first cladding layer 202, the non-doped active layer 203, the p-type second cladding layer 204, the p-type first etching stop layer 205,
A p-type second etching stop layer 206 and an n-type current / light confinement layer 207 are laminated.

Next, a stripe-shaped groove is formed in the central portion of the current / light confinement layer 205 using the first etching solution so as to reach the p-type second etching stop layer 206, and the second etching solution is further formed. Using, the stripe-shaped groove is formed so as to reach the p-type first etching stop layer 205. A p-type third cladding layer 209 is formed by the second MOCVD method, the liquid phase epitaxy (LPE) method, or the molecular beam epitaxy (MBE) method so as to fill the groove 208. Subsequently, the p-type contact layer 210 is laminated and formed.

After that, a p-type electrode 211 is formed on the upper surface of the contact layer 210, and an n-type electrode 212 is formed on the lower surface of the substrate 201. The cavity length is adjusted to 200 μm by the cleavage method, and the reflectance of the cavity facet is adjusted. Of Al ₂ O ₃ to be 30%
Form a film.

Like the semiconductor laser device of the first embodiment, the semiconductor laser device of the second embodiment has a larger characteristic temperature than the conventional semiconductor laser device using Se as the dopant of the n-type current / light confinement layer. Since the increase in current at high temperature is suppressed, the device life at high temperature operation is improved three times or more.

In this embodiment, the first etching stop layer 205 and the second etching stop layer 206 are also included.
Since the stripe groove 208 is formed, the depth of the stripe groove 208 can be precisely controlled, and the surface of the groove 208 can be made of GaAs which is difficult to be oxidized. Since the layer thicknesses of the first etching stop layer 205 and the second etching stop layer 206 can be made sufficiently smaller than those of the adjacent p-type second cladding layer 204 and n-type current / light confinement layer 207, the etching stop layer should be formed. Therefore, the device characteristics are not adversely affected. In addition, 2 for groove filling
The LPE method or the MBE method can also be used in the second growth.

(Third Embodiment) FIG. 4 shows a sectional view of a semiconductor laser device according to a third embodiment.

In this semiconductor laser device, an n-type Al _0.5 Ga _0.5 As first cladding layer 302 (layer thickness 1.5 μm, carrier concentration 7 × 10 ¹⁷ cm) is formed on an n-type GaAs substrate 301.
^-3 , dopant Se), non-doped Al _0.14 Ga _0.86 A
s active layer 303 (layer thickness 0.05 μm), p-type Al _0.5 G
a _0.5 As second cladding layer 304 (layer thickness 0.4 μm, carrier concentration 1 × 10 ¹⁸ cm ⁻³ , dopant Zn) and n-type Al _0.7 Ga _0.3 As current / light confinement layer 305 (layer thickness 1.0 μm, carrier concentration 7 × 10 ¹⁷ cm ⁻³ , dopant Si) is formed.

A stripe-shaped groove 306 is formed in the center of the n-type current / light confinement layer 305 so as to reach the p-type second cladding layer 304, and the p-type Al _0.5 Ga _0.5 As is filled in the groove 306. A third clad layer 307 (layer thickness 1.5 μm) is formed. On top of that, p-type G
An aAs contact layer 308 (layer thickness 1.5 μm) is formed.

Furthermore, p is formed on the p-type contact layer 308.
A mold electrode 309 is formed, and an n-type electrode 310 is formed on the n-type GaAs substrate 301 side.

This semiconductor laser device can be manufactured as follows.

First, on the n-type GaAs substrate 301, the first
The n-type first cladding layer 30 is formed by the MOCVD method for the first time.
2, non-doped active layer 303, p-type second cladding layer 30
4. The n-type current / light confinement layer 305 is formed by stacking.

Next, a stripe-shaped groove 306 is formed in the central portion of the current / light confinement layer 305 so as to reach the p-type second cladding layer 304, and the second MOCVD method is performed so as to fill this groove 306. Thus, the p-type third cladding layer 307 is formed, and then the p-type contact layer 308 is laminated.

Thereafter, a p-type electrode 309 is formed on the upper surface of the contact layer 308 and an n-type electrode 310 is formed on the lower surface of the substrate 301, and the cavity length is adjusted to 375 μm by the cleavage method, and the light emitting side of the cavity is formed. Al ₂ O ₃ film and Si so that the reflectivity of the end face is 12% and the reflectivity of the opposite end face is 75%.
Form a film.

In the semiconductor laser device of this embodiment, the bandgap of the current / light confinement layer 305 is larger than that of the active layer 303, and the light generated in the active layer 303 is not absorbed by the current / light confinement layer 305. In this case, since the refractive index of the current / light confinement layer 305 is smaller than the surrounding refractive index, light is mainly confined in the active layer immediately below the stripe groove 306 due to the difference in refractive index. In this semiconductor laser device, a p-type electrode 309 and an n-type electrode 310
The threshold current when a forward voltage is applied between
mA, current-optical output characteristic slope efficiency is 0.80 W /
A.

Room temperature 20 of the semiconductor laser device of this embodiment
Table 2 below shows characteristic temperatures at 70 ° C. and 70 ° C., and device life when light output of 50 mW is performed at 70 ° C.
Shown in Further, as a comparative example, the current / light confinement layer 305
A conventional semiconductor laser device containing Se as a dopant is also shown.

[0071]

[Table 2]

In Table 2 above, the characteristic temperature T0 is 70
The following formula (2) is obtained from the ratio of the threshold current Ith (70 ° C.) at 20 ° C. and the threshold current Ith (20 ° C.) at 20 ° C.
Is defined as The larger T0 is, Ith (70
The ratio of (° C.) to Ith (20 ° C.) becomes close to 1, and the increase in current at high temperature is suppressed.

Ith (70 ° C.) / Ith (20 ° C.) = Exp {(70 ° C.-20 ° C.) / T0} (2) Further, the device lifetime is the operating current of the semiconductor laser device at the initial operating current. It is the running time when it increases by 20%.

As can be understood from Table 2 above, the semiconductor laser device of the third embodiment has a large characteristic temperature and a high temperature as compared with the conventional semiconductor laser device using Se as the dopant of the n-type current / light confinement layer. Since the increase in current during the operation is suppressed, the device life during high temperature operation is improved five times or more.

The reason why such a result is obtained is considered as follows.

As described in the first embodiment, the characteristic temperature of the semiconductor laser device depends on the carrier concentration of the p-type second cladding layer 304. In the manufacture of the semiconductor laser device of this embodiment, the carrier concentration of the n-type current and light confinement layer 305 at the end of the first MOCVD growth is changed so that the carrier concentration and the layer thickness of the p-type second clad layer 304 are changed. The result of measuring the relationship is shown in FIG.

In the semiconductor laser device of this embodiment, as shown in FIG. 5, the carrier concentration of the p-type second cladding layer 304 decreases during growth, but the degree of decrease is smaller than that of the conventional semiconductor laser device. Clearly few. This is because diffusion of the dopant Zn of the p-type second cladding layer 304 to the adjacent layer was suppressed by using Si as the dopant of the n-type current / light confinement layer 305.

In the semiconductor laser device of this embodiment,
The carrier concentration of the p-type second cladding layer 304 is set to 5 × 10 ¹⁷
In order to make it cm ⁻³ or more, the carrier concentration of the n-type current and light confinement layer 305 containing the dopant Si is 5 × 10 ¹⁸ c.
It may be m ^-3 or less. In addition, the n-type current / light confinement layer 3
The bandgap of 05 is larger than the bandgap of the active layer 303, and the light generated in the active layer 303 is not absorbed by the n-type current / light confinement layer 305. Therefore, in order to sufficiently confine the current, the n-type current / light confinement layer 105 The carrier concentration of 1 × 10 ¹⁷ cm ⁻³ or more. And p
The layer thickness of the mold second clad layer 304 is 0.05 μm or more and 0.6 μm or more in order to sufficiently confine current and light.
It is preferably m or less.

As shown in FIG. 5, in the semiconductor laser device of this embodiment, the carrier concentration of the n-type current and light confinement layer 305 is 1 × 10 ¹⁷ cm ⁻³ or more and 5 × 10 ¹⁸ cm ⁻³ or less, and the p-type The p-type second cladding layer 30 is provided under the condition that the layer thickness of the second cladding layer 304 is 0.05 μm or more and 0.6 μm or less.
The carrier concentration of No. 4 can be 5 × 10 ¹⁷ cm ⁻³ or more.

Therefore, the leakage of carriers from the active layer 303 to the p-type second cladding layer 304 at high temperature can be suppressed, the high temperature operating current can be reduced, and the device life at high temperature can be improved. In this case, the n-type current / light confinement layer 30
The carrier concentration of No. 5 is sufficiently high, and the current can be sufficiently confined. The layer thickness of the p-type second cladding layer 304 is a thickness suitable for confining current and light.

Further, in the semiconductor laser device according to the third embodiment, the n-type first cladding layer 30 adjacent to the active layer 303.
Se is used as the second dopant without using Si. The Se dopant does not reduce the emission efficiency even if it diffuses from the n-type first cladding layer 302 to the active layer 303, and thus it is possible to prevent the deterioration of the semiconductor laser device characteristics.

(Embodiment 4) FIG. 6 is a sectional view of a semiconductor laser device according to Embodiment 4.

In this semiconductor laser device, an n-type Al _0.5 Ga _0.5 As first cladding layer 402 (layer thickness 1.5 μm, carrier concentration 1 × 10 ¹⁸ cm) is formed on an n-type GaAs substrate 401.
^-3 , dopant S), non-doped MQW (single quantum well) AlGaAs active layer 403 (3 wells, well layer thickness 0.01 μm, well Al composition ratio 0.1, barrier layer thickness 0.008 μm, barrier Al composition ratio) 0.35, guide layer thickness 0.02 μm, guide Al composition ratio 0.35) and p
Type Al _0.5 Ga _0.5 As second cladding layer 404 (layer thickness 1.
5 μm, carrier concentration 6 × 10 ¹⁷ cm ⁻³ , dopant M
g) has been formed.

The p-type second cladding layer 404 is etched so that the central portion thereof has a ridge stripe shape,
The remaining thickness other than the ridge stripe shape is 0.20 μm. Hereinafter, the ridge stripe-shaped portion of the p-type second cladding layer 404 will be referred to as the third cladding layer 406, and the other flat portion will be referred to as the p-type second cladding layer 404.

On the p-type third cladding layer 406, p-type G
An aAs cap layer 405 (layer thickness of 0.1 μm) is formed, and the n-type GaAs current / light confinement layer 407 (layer is formed so as to be embedded so as to sandwich both outer sides of the ridge stripe-shaped third cladding layer 406 and the p-type cap layer 405. Thickness 0.5
μm, carrier concentration 3.5 × 10 ¹⁸ cm ⁻³ , and dopant Si) are formed.

On top of that, p-type Ga is formed so as to cover the entire surface of the substrate.
An As contact layer 408 (layer thickness 1.5 μm) is formed. Further, a p-type electrode 409 is formed on the p-type contact layer 408, and n is formed on the n-type GaAs substrate 401 side.
A mold electrode 410 is formed.

This semiconductor laser device can be manufactured as follows.

First, on the n-type GaAs substrate 401, the first
The n-type first cladding layer 40 is formed by the MOCVD method for the second time.
2. The non-doped MQW active layer 403, the p-type second clad layer and the p-type cap layer are laminated.

Next, a SiN film is formed in a stripe shape,
The p-type second clad layer and the p-type cap layer are etched using this as a mask to obtain a p-type second clad layer 404 and a ridge stripe-shaped third clad layer 406.
And a p-type cap layer 405 is formed. At this time, p
The residual thickness of the mold second clad layer 404 is set to 0.2 μm.

Then, using the striped SiN film as a mask, a second MO is formed on both outer sides of the ridge stripe.
The n-type current and light confinement layer 407 is embedded and grown by the CVD method.

Next, the SiN film is removed, and the third M
A p-type contact layer 408 is laminated and formed by the OCVD method so as to cover the entire surface of the substrate.

After that, a p-type electrode 409 is formed on the upper surface of the contact layer 408, and an n-type electrode 410 is formed on the lower surface of the substrate 401. The cavity length is adjusted to 400 μm by the cleavage method, and the light emitting side of the cavity is formed. The Al ₂ O ₃ film and Si so that the reflectance of the end face is 10% and the reflectance of the opposite end face is 90%.
Form a film.

In the semiconductor laser device of this embodiment, the band gap of the current / light confinement layer 407 is less than or equal to the band gap of the active layer 403. Therefore, the light generated in the active layer 403 is absorbed by the current / light confinement layer 405, and the light is mainly confined in the active layer immediately below the ridge stripe. In this semiconductor laser device, the threshold current was 40 mA when a forward voltage was applied between the p-type electrode 409 and the n-type electrode 410, and the slope efficiency of the current-light output characteristics was 0.6 W / A. .

Room temperature 20 of the semiconductor laser device of this embodiment
Table 3 below shows the characteristic temperatures at 70 ° C. and 70 ° C. and the device life when an optical output of 50 mW is performed at 70 ° C.
Shown in As a comparative example, the current / light confinement layer 405
A conventional semiconductor laser device containing Se as a dopant is also shown.

[0095]

[Table 3]

In Table 3 above, the characteristic temperature T0 is 70
By the ratio of the threshold current Ith (70 ° C.) at 20 ° C. and the threshold current Ith (20 ° C.) at 20 ° C., the following formula (3)
Is defined as The larger T0 is, Ith (70
The ratio of (° C.) to Ith (20 ° C.) becomes close to 1, and the increase in current at high temperature is suppressed.

Ith (70 ° C.) / Ith (20 ° C.) = Exp {(70 ° C.-20 ° C.) / T0} (3) Further, the device lifetime is the operating current of the semiconductor laser device at the initial operating current. It is the running time when it increases by 20%.

As can be understood from Table 3 above, the semiconductor laser device of the fourth embodiment has a characteristic temperature larger than that of the conventional semiconductor laser device and suppresses an increase in current at high temperatures. The element life of is improved more than 5 times.

The reason why such a result is obtained can be considered as follows.

As described in the first embodiment, the characteristic temperature of the semiconductor laser device depends on the carrier concentration of the p-type second cladding layer 404. In the manufacture of the semiconductor laser device of this embodiment, the carrier concentration of the n-type current / light confinement layer 405 at the end of the second MOCVD growth is changed to change the p-type second cladding layer 404 (flat portion other than the ridge stripe). The result of measurement of the relationship between the carrier concentration and the layer thickness is shown in FIG.

In the semiconductor laser device of this embodiment, as shown in FIG. 7, the carrier concentration of the p-type second cladding layer 404 decreases during growth, but the degree of decrease is lower than that of the conventional semiconductor laser device. Clearly few. This is because diffusion of the dopant Mg of the p-type second cladding layer 404 to the adjacent layer was suppressed by using Si as the dopant of the n-type current and light confinement layer 407.

In the semiconductor laser device of this embodiment,
The carrier concentration of the p-type second cladding layer 404 is set to 5 × 10 ¹⁷
In order to make it cm ⁻³ or more, the carrier concentration of the n-type current and light confinement layer 405 containing the dopant Si is 5 × 10 ¹⁸ c.
It may be m ^-3 or less. In addition, the n-type current / light confinement layer 4
Since the bandgap of 07 is less than the bandgap of the active layer 403, in order to sufficiently confine the current, n
-Type current / light confinement layer 407 has a carrier concentration of 1 × 10 ¹⁸
It must be at least cm ^-3 . Further, the layer thickness of the p-type second cladding layer 404 (portion other than the ridge stripe) is 0.05 in order to sufficiently confine current and light.
It is desirable that the thickness is at least μm and at most 0.6 μm.

As shown in FIG. 7, in the semiconductor laser device of this embodiment, the carrier concentration of the n-type current and light confinement layer 407 is 1 × 10 ¹⁷ cm ⁻³ or more and 5 × 10 ¹⁸ cm ⁻³ or less, and the p-type The p-type second cladding layer 40 is provided under the condition that the layer thickness of the second cladding layer 404 is 0.05 μm or more and 0.6 μm or less.
The carrier concentration of No. 4 can be 5 × 10 ¹⁷ cm ⁻³ or more.

Therefore, the leakage of carriers from the active layer 403 to the p-type second cladding layer 404 at high temperature can be suppressed to reduce the high temperature operating current, and the device life at high temperature can be improved. In this case, the n-type current / light confinement layer 40
The carrier concentration of No. 7 is sufficiently high, and the current can be sufficiently confined. Further, the layer thickness of the p-type second cladding layer 404 (portion other than the ridge stripe) is a thickness suitable for confining current and light.

Furthermore, in the semiconductor laser device of the third embodiment, the n-type first cladding layer 40 adjacent to the active layer 403 is used.
S is used as the second dopant without using Si.
The S dopant does not reduce the emission efficiency even if it diffuses from the n-type first cladding layer 402 to the active layer 403, so that the characteristics of the semiconductor laser device can be prevented from being degraded.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments.

The layer thickness, Al composition ratio, and carrier concentration of each semiconductor layer may be other than those shown in the embodiment.

As the growth method, other than the MOCVD method, other methods such as MBE method, LPE method, MOMBE method, ALE (atomic beam epitaxial) method may be used.

Zn or Mg is used as the p-type dopant.
Can be used, and as the n-type dopant contained in the first cladding layer, a group VI atom other than Si (Se, S,
Te, etc.) can be used.

In the above embodiment, AlGaAs / GaA is used.
Although the present invention is applied to the s-based material, it is also applicable to other materials, for example, AlGaInP / GaA.
s-based materials can be used.

[0111]

As is apparent from the above description, according to the present invention, S is used as the dopant for the n-type current / light confinement layer.
By using i, it is possible to prevent the dopant of the p-type cladding layer from diffusing during the growth of the n-type first cladding layer, the active layer, the p-type second cladding layer, and the n-type current / light confinement layer on the n-type substrate. Can be suppressed. Since the carrier concentration of the p-type clad layer can be prevented from decreasing, the barrier height of the p-type clad layer with respect to the active layer can be sufficiently maintained and the leakage of carriers from the active layer to the p-type clad layer can be prevented. .
Since it is possible to suppress the current increase that occurs remarkably during high temperature operation,
The device life in high temperature operation can be improved.

Further, since Si is not used as the dopant of the n-type first cladding layer adjacent to the active layer,
Even if the dopant of the n-type first cladding layer diffuses into the active layer, the luminous efficiency does not decrease, and it is possible to prevent the deterioration of the device characteristics due to this.

In particular, the thickness of the p-type second cladding layer is 0.0
When the thickness is 5 μm or more and 0.6 μm or less, current and light can be efficiently confined.

Further, the band gap of the n-type current / light confinement layer is set to be equal to or less than the band gap of the active layer, and the carrier concentration of the light confinement layer is 1 × 10 ¹⁸ cm ⁻³ or more and 5 × 10 ¹⁸ cm.
^-3 or less, or the band gap of the n-type current / light confinement layer is made larger than that of the active layer, and the carrier concentration of the current / light confinement layer is 1 × 10 ¹⁷ cm ⁻³ or more and 5 × 10 ¹⁸ cm ^−3. In the following cases, the current and light can be sufficiently confined and the carrier concentration of the p-type second cladding layer can be sufficiently increased.

Furthermore, when a group VI atom such as Se, S, or Te is used as the dopant of the first cladding layer, the luminous efficiency is not lowered, and thus the deterioration of the device characteristics can be prevented.

The semiconductor laser device having good characteristics as described above can be suitably used for an optical disk or the like.

[Brief description of drawings]

FIG. 1 is a sectional view of a semiconductor laser device according to a first embodiment.

FIG. 2 is a graph showing the relationship between the carrier concentration and the layer thickness of the p-type second cladding layer in the semiconductor laser device of the first embodiment.

FIG. 3 is a sectional view of a semiconductor laser device according to a second embodiment.

FIG. 4 is a sectional view of a semiconductor laser device according to a third embodiment.

FIG. 5 is a graph showing the relationship between the carrier concentration of the p-type second cladding layer and the layer thickness of the semiconductor laser device according to the third embodiment.

FIG. 6 is a sectional view of a semiconductor laser device according to a fourth embodiment.

FIG. 7 is a graph showing the relationship between the carrier concentration of the p-type second cladding layer and the layer thickness of the semiconductor laser device according to the fourth embodiment.

FIG. 8 is a sectional view of a conventional semiconductor laser device.

FIG. 9 is a graph showing the relationship between the carrier concentration and the layer thickness of the p-type second cladding layer in the conventional semiconductor laser device.

[Description of Reference Signs] 101, 201, 301, 401 n-type GaAs substrate 102, 202, 302, 402 n-type first clad layer 103, 203, 303, 403 active layer 104, 204, 304, 404 p-type second clad layer Layers 105, 207, 305, 407 N-type current / light confinement layers 106, 208, 306 Stripe-shaped grooves 107, 209, 307, 406 p-type third cladding layers 108, 210, 308, 408 p-type contact layers 109, 211, 309, 409 p-type electrode 110, 212, 310, 410 n-type electrode 205 p-type first etching stop layer 206 p-type second etching stop layer 405 p-type cap layer

Claims (6)

[Claims] 1. An n-type first clad layer, an active layer, and a p-type second clad layer are formed in this order from the substrate side on an n-type semiconductor substrate, and stripe-shaped groove portions are formed on the second clad layer. In the semiconductor laser device in which the n-type current / light confinement layer has and the p-type third cladding layer is formed so as to fill the stripe-shaped groove portion, the current / light confinement layer contains Si as a dopant,
A semiconductor laser device wherein the first cladding layer does not contain Si as a dopant. 2. An n-type first clad layer, an active layer, and a p-type second clad layer are formed in this order from the substrate side on an n-type semiconductor substrate, and a ridge stripe pattern is formed on the second clad layer. In a semiconductor laser device in which a p-type third clad layer is formed and an n-type current / light confinement layer is formed so as to sandwich both sides of the ridge stripe-shaped third clad layer, the current / light confinement layer serves as a dopant. Contains
A semiconductor laser device wherein the first cladding layer does not contain Si as a dopant. 3. The thickness of the second cladding layer is 0.05 μm.
The semiconductor laser device according to claim 1, wherein the semiconductor laser device has a size of m or more and 0.6 μm or less. 4. The band gap of the current / light confinement layer is equal to or less than the band gap of the active layer, and the carrier concentration of the current / light confinement layer is 1 × 10 ¹⁸ cm ⁻³ or more and 5 × 1.
The semiconductor laser device according to claim 1, 2 or 3, which has a ^{density of} 0 ¹⁸ cm ^-3 or less. 5. The band gap of the current / light confinement layer is larger than the band gap of the active layer, and the carrier concentration of the current / light confinement layer is 1 × 10 ¹⁷ cm ⁻³ or more and 5 × 1.
The semiconductor laser device according to claim 1, 2 or 3, which has a ^{density of} 0 ¹⁸ cm ^-3 or less. 6. The semiconductor laser device according to claim 1, wherein the dopant of the first cladding layer is a group VI atom.